1. Field of the Invention
This invention relates to a method for decreasing kogation on the surface of a heater for application of heat to the ink, a method for ink-jet recording, an ink-jet recording apparatus, a recording unit, and a method for increasing the life of the ink-jet recording head.
2. Related Background Art
The have been proposed various types of ink-jet recording methods. According to one ink-jet recording method, such as the so-called bubble-jet recording method described in, for example, Japanese Patent Application Laid-Open No. 54-51837, ink is ejected in the form of ink droplets by the action of thermal energy. A feature of this ink-jet method is that high quality images can be formed on plain paper having no special coating layer at high speed and at low cost, due to the very simple structure of the high-density multiple nozzles.
In this recording method, rapid heating of the heater in the recording head induces bubble generation in the liquid on the heater with rapid bubble volume inflation, and the action force due to this rapid volume increase ejects a liquid droplet from the nozzle arranged at the tip of the recording head to make the droplet fly to the recording material and attach thereon. Recording is thus carried out. In this method, however, the heater in the recording head is repeatedly heated to eject ink during printing. This may cause the deposition of the decomposition product of the ink, so-called xe2x80x9ckogaxe2x80x9d (scorch), on the surface of the heater. Deposition of koga prevents the efficient transmission of the thermal energy from the heater to the ink, resulting in decrease in the volume and speed of the ejected droplets in comparison with the initial stage, which affects the image quality. In such a case, the recording head must be changed with a new one in order to continuously achieve high quality printing. To the users, this means a total higher printing cost. Thus, reduction of kogation on the heater in order to prolong the recording head life has been one of the important technical problems to be addressed in the art of bubble-jet recording.
There has been proposed, for example, ink containing an oxoanion (Japanese Patent Application Laid-Open No. 3-160070), such as phosphate salts, polyphosphates, phosphate esters, arsenates, molybdates, sulfates, sulfites and oxalates.
An object of the present invention is to provide a method for decreasing kogation on the surface of the heater used for applying thermal energy to the ink in a recording head so as to eject the above ink from the recording head.
Another object of the present invention is to provide an ink-jet recording apparatus which enables high quality printing and prolonged product life of the recording head.
A further object of the present invention is to provide a recording unit which enables high quality printing over a prolonged period.
Still another object of the present invention is to provide a method for prolonging the product life of the recording head to lower the cost in high quality printing.
According to one aspect of the present invention, there is provided a method for alleviating kogation on a surface of a heater of a recording head of an ink-jet printer, the heater being arranged to apply thermal energy to ink in the recording head to eject the ink from an opening in the recording head, and the heater having an outermost protection layer containing at least a metal or oxide thereof, wherein the ink comprises the following components:
(a) a coloring material;
(b) a liquid medium; and
(c) at least one compound selected from the group consisting of aldaric acids and aldarates.
Such an arrangement makes possible a very effective reduction in kogation on the outermost protection layer of the heater. Although the reason why the use of this ink brings about good results is not unknown, it may be due to the interaction between the aldaric acid and/or aldarate with the metal and/or metal oxide constituting the outermost protection layer of the above heater, which interaction may prevent kogation or promote the decomposition of koga or peeling of koga from the heater surface.
When the metal or the metal oxide contained in the outermost protection layer of the heater is tantalum or an oxide thereof, the effect is more remarkable. Further, the effect of the present invention in preventing kogation improves if the amount of the energy applied to the above heater is set so that Eop satisfies the following relation:
1.10xe2x89xa6Eop/Ethxe2x89xa61.50,
wherein Eop denotes the amount of the energy applied to the above heater and Eth the minimum energy required for ink ejection.
According to another aspect of the present invention, there is provided an ink-jet recording method comprising the steps of:
applying pulse electric signals to a heater in an ink flow path of a recording head according to recording signals,
generating heat from the heater to heat ink in the ink flow path and ejecting the ink from an opening, wherein the ink comprises the following components:
(a) a coloring material;
(b) a liquid medium; and
(c) at least one compound selected from the group consisting of aldaric acids and aldarates.
According to a further aspect of the present invention, there is provided an ink-jet recording apparatus comprising:
an ink storing portion storing ink;
an ink-jet recording head provided with a heater for applying thermal energy to the ink introduced in an ink flow path from the ink storing portion; and
means for applying electrical pulse signals to the heater in response to recording information, wherein the heater has an outermost protection layer containing at least one of a metal and an oxide thereof, and the ink comprises the following components:
(a) a coloring material;
(b) a liquid medium; and
(c) at least one compound selected from the group consisting of aldaric acids and aldarates.
According to still another aspect of the present invention, there is provided a recording unit comprising an ink storing portion for storing ink and an ink-jet recording head portion for ejecting the ink through an opening by thermal energy action, the ink-jet recording head being provided with a heater for applying thermal energy to the ink, the heater having an outermost protection layer containing at least a metal or oxide thereof, wherein the ink comprises the following components:
(a) a coloring material;
(b) a liquid medium; and
(c) at least one compound selected from the group consisting of aldaric acids and aldarates.
According to still another aspect of the present invention, there is provided a method for prolonging a life of a recording head equipped with a heater, the recording head being used in an ink-jet recording method comprising a step of ejecting ink through an opening by applying thermal energy to the ink,
wherein the heater is provided with an outermost protection layer containing at least a metal or oxide thereof and the ink comprises the following components:
(a) a coloring material;
(b) a liquid medium; and
(c) at least one compound selected from the group consisting of aldaric acids and aldarates.